This invention relates generally to surgical devices and procedures, and more specifically to an improvement in surgically implanted devices for expanding skin, mucus membrane, and other body tissues.
Tissue expansion is now a recognized modality of treatment in reconstructive surgery. It is based upon the following principle: Skin or mucus membrane reacts to a slowly enlarging mass beneath it by increasing in surface area. This is naturally-occurring phenomenon, most frequently displayed by the increase of abdominal surface area during pregnancy. Progressive obesity also illustrates this phenomenon.
One device developed by C. Radovan, causes this expansion phenomenon by means of an inflatable bag surgically implanted beneath the skin. The bag is connected by a tube to a reservoir which is also implanted. The bag is then incrementally inflated by hypodermically injecting a fluid into the reservoir from time to time. Inflation of the implant results in an increase in the surface area of overlying tissue. At a second operation, this implant is removed, and the overlying redundant tissue is utilized for reconstructive purposes. In some situations it may be stretched into a new position as a flap. In other situations, such as breast reconstruction, the tissue expander may be implanted beneath the skin at the site of the previously removed breast and simply replaced by a standard breast implant when expansion has been completed.
U.S. Pat. No. 4,217,889 in the names of C. Radovan and R. Schulte illustrates this type of device. There are also U.S. Pat. Nos. 4,190,040 and 3,310,051 which relate to this general subject.
The tissue expansion technique has been shown by the applicant to result in an increase in the reproduction rate of overlying skin; thus stimulation of new tissue is actually produced, rather than a simple "borrowing" of tissue from one area to another. In addition, because this expanded tissue is derived from immediately adjacent tissue, color and texture matching is optimized. Hair-bearing characteristics are also preserved. Finally, tissue expansion has been shown to result in a marked increase in blood supply to the expanded area; thus the tissue is made more desirable for reconstructive surgical purposes.
A second type of tissue expander, developed by R. Lapin differs physically from the Radovan implant in one significant way: The reservoir, by which injections are made, is located in the dome of the implant. Thus, the Lapin implant is slightly more compact, and does not require a connector tube.
A third type of tissue expander has been developed by the applicant. This is a self-inflating implant which is osmotically powered. The implant inflates over time at a predictable rate, via an influx of extracellular water. A hypertonic implant interior causes this influx.
The devices and procedures of Radovan have certain disadvantages, some of which have been described previously in applicant's prior U.S. Pat. No. 4,157,085. In addition, two new disadvantages of the devices and procedures of Radovan and Lapin have been identified and are described as follows.
The inflatable bag used in both the Lapin and Radovan expanders is made of medical-grade silicone of varying thickness from 10 mil (10/1000 inch) to 25 mil (25/1000 inch). When deflated and placed beneath the skin or mucus membrane, neither bag is readily compressed. Folding the bag upon itself results in multiple wrinkles and acute creases of the membrane. These irregular and unpredictable folds and creases gradually unfurl as the bag is inflated. However, in the early stages of inflation, three major problems arise from the presence of these folds and creases: First, the implanted device is unsightly due to multiple irregularities of the skin or mucosal surface caused by the folded bag. Second, these folds and creases create potential stress points within the membrane, which are subject to tearing and perforation (fold fault). Third, these folds and creases of the membrane cause untoward focal pressure on overlying soft tissue, and they may result in erosion of this tissue. Such erosion is catastrophic in that it results in potential bacterial contamination of the entire implant site which, if it were to occur, would usually necessitate implant removal and abandonment of the procedure.
A further major disadvantage of both the Radovan and Lapin devices relates to their inability to be readily modified, at the time of surgery, to meet the requirements and dimensions of some wounds. The bases of both types of implants are either circular or rectangular, depending on the style of implant selected, while the reconstruction may be best served by an expander of less standard conformation, such as a triangle, rhomboid, or semi-annulus.
The present invention is directed to a new and improved tissue expander overcoming the disadvantages of the prior art, particularly as described above with reference to the Lapin and Radovan expanders. Accordingly, one important advantage of the present invention is that skin tissue and mucus membrane can be more safely and aesthetically expanded.
Another advantage of the invention is that the tissue expander can be more conveniently implanted by the surgeon and adapted to the particular needs of any given patient for surgical reconstructive procedures.
The present invention in its preferred form is embodied by a relatively rigid base on which is disposed a flat envelope which, when uninflated, projects a smooth surface of minimal cross sectional height toward the undersurface of overlying tissue when implanted. The material of the envelope is expansible by stretching such that in response to introduction of expansion fluid, the envelope expands by stretching to exert a more uniform expansion force to the overlying tissue so as to alleviate the problems of prior art devices referred to above.
Moreover, as will be subsequently explained in greater detail, the envelope may comprise a single thickness layer of material whose perimeter is secured to the perimeter of the base so that both envelope and base define the expansion space which is expanded by the introduction of fluid. In another embodiment, means are provided for separably mounting the envelope on the base and with the envelope itself defining the expansion space and taking the form of a double thickness of said material disposed on and flat against the base when in the uninflated condition. In the last mentioned embodiment, the base may be cut from base material into a desired shape for use by the surgeon at his discretion in establishing the best shape for the tissue expander. The envelope, by being removably mountable on the base, can be readily conformed to the shape of the base which has been cut by the surgeon. In this way the tissue expander of the present invention in one aspect can be readily conformed to different shapes most suitable for the needs of any given patient.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.